1. Field of the Invention
The present invention relates to a method for injecting a fluid into an oil and or gas reservoir or formation
2. Background of the Invention
More particularly, the invention relates to a method using an autonomous valve or flow control device in injectors in oil production, said valve or flow control device being described in patent application No. 20063181 withdrawn before publication and in International application No. PCT/NO2007/000204 claiming priority from NO 20063181 and which is not yet published at the date of filing of the present application.
Devices for recovering of oil and gas from long, horizontal and vertical wells are known from U.S. Pat. Nos. 4,821,801, 4,858,691, 4,577,691 and GB patent publication No. 2169018. These known devices comprise a perforated drainage pipe with, for example, a filter for control of sand around the pipe. A considerable disadvantage with the known devices for oil/and or gas production in highly permeable geological formations is that the pressure in the drainage pipe increases exponentially in the upstream direction as a result of the flow friction in the pipe. Because the differential pressure between the reservoir and the drainage pipe will decrease upstream as a result, the quantity of oil and/or gas flowing from the reservoir into the drainage pipe will decrease correspondingly. The total oil and/or gas produced by this means will therefore be low. With thin oil zones and highly permeable geological formations, there is further a high risk that of coning, i.e. flow of unwanted water or gas into the drainage pipe downstream, where the velocity of the oil flow from the reservoir to the pipe is the greatest.
From World Oil, vol. 212, N. 11 (11/91), pages 73-80, is previously known to divide a drainage pipe into sections with one or more inflow restriction devices such as sliding sleeves or throttling devices. However, this reference is mainly dealing with the use of inflow control to limit the inflow rate for up hole zones and thereby avoid or reduce coning of water and or gas.
WO-A-9208875 describes a horizontal production pipe comprising a plurality of production sections connected by mixing chambers having a larger internal diameter than the production sections. The production sections comprise an external slotted liner which can be considered as performing a filtering action. However, the sequence of sections of different diameter creates flow turbulence and prevent the running of work-over tools.
When extracting oil and or gas from geological production formations, fluids of different qualities, i.e. oil, gas, water (and sand) is produced in different amounts and mixtures depending on the property or quality of the formation. None of the above-mentioned, known devices are able to distinguish between and control the inflow of oil, gas or water on the basis of their relative composition and/or quality.
With the autonomous valve as described in NO 20063181 and PCT/NO2007/000204 is provided an inflow control device which is self adjusting or autonomous and can easily be fitted in the wall of a production pipe and which therefore provide for the use of work-over tools. The device is designed to “distinguish” between the oil and/or gas and/or water and is able to control the flow or inflow of oil or gas, depending on which of these fluids such flow control is required.
The device as disclosed in NO 20063181 and PCT/NO2007/000204 is robust, can withstand large forces and high temperatures, prevents draw dawns (differential pressure), needs no energy supply, can withstand sand production, is reliable, but is still simple and very cheap.
As to prior art technology, injector wells in oil reservoirs are used to increase oil recovery (IOR) and/or enhanced oil recovery (EOR). Injectors can be used to inject e.g. water, steam, hydrocarbon gas and/or CO2. The injector wells may have different orientation and extent. In many situations the injected fluid should be evenly distributed in the reservoir. In these cases long injection wells are used, and the injected fluids are injected in different sections along the well.
When injecting fluid in different sections along a well the injection will be non-uniform (see FIG. 10). This is mainly caused by the non-uniform reservoir which may include e.g. high and low permeable zones, fractures and short-cuts. The nature of all fluid flow is that the fluid will flow where the resistance is smallest. This fact ensures that the injections will, most often, be very non-uniform. This result in poor utilization of injected fluid and low IOR/EOR effect.